This invention relates to disc lasers and more particularly to face pumped disc lasers.
A laser is a device consisting of a rod of laser material between parallel end mirrors, one of which provides full reflection and the other partial reflection and partial transmission of radiation therethrough. Pump light is introduced into the laser material and laser energy is produced in the laser rod by photonic emission from high energy level ions in the laser material. Pump light increases the number of ions from a lower energy level to an upper energy level. Pump light energy depletes the lower level population of ions creating an inversion of energy states and some of the ions in the upper energy undergo a spontaneous light emissive transmission to the lower level and a portion of the spontaneously emissive light reflects back and forth between the mirrored surfaces stimulating similar light emissive transmissions from other upper level ions. The stimulated emissions which reflect back and forth through the rod generates highly intensive laser light energy which is emitted through the partially reflective mirror.
One of the problems associated with the production of a laser beam is that the pumping light produces heat in the laser material as does operation at high repetition rates and thus, means often must be provided for removing excess heat. Excessive heat can reduce efficiency, produce an undesirable lens effect in the rod or cause fracture of the rod. One method proposed to solve this excessive heat problem was to segment the laser rod into a number of discs. By doing this the minimum dimension of each disc can be made small enough to eliminate thermal fracture. Also, it is possible to pass a cooling fluid past each of the discs to reduce the heating thereof.
However, more segmenting of the rod into thin discs presents certain problems. First of all, the pumping energy is applied to the edge of the discs rather than the faces thereof and therefore large cylindrical stresses are induced in the discs and these are relatively complex to compensate. Also, edge pumped discs are very inefficient.
In order to improve the efficiency of disc lasers it has been proposed to incline the discs at an angle with respect to the laser beam and insert prisms between the discs such that pump light is allowed to fall directly on the faces of the discs. However, this method establishes a preferred polarization direction in the laser cavity. Also, when uniaxial or biaxial laser crystals are employed as the laser medium, the crystalline axes must be properly orientated with respect to the Brewster angle or otherwise high loses due to birefringence would be produced. Furthermore, the faces of the prisms through which the laser beam passes are not normal to the laser beam and therefore extreme care must be taken in fabricating these prisms (e.g., costly high quality polishing) to ensure that the prisms will not cause dispersion of the laser beam.